1. Field of the Invention
The invention relates to an optical system and a display apparatus, and particularly relates to an illumination system and a projection apparatus.
2. Description of Related Art
Recently, projection apparatuses using solid-state optical sources such as light emitting diodes (LED) and laser diodes have a more and more important role on the market. Also, laser diodes have a 20% higher light emitting efficiency. In order to break through the limitation on the optical source of the LEDs, a pure-color optical source for a projector generated by using a laser source to excite phosphor has been developed. Besides, in addition to using a laser source to excite phosphor, a laser projection apparatus may also directly use a laser beam as an illumination optical source of the projector and has the advantage of adjusting a number of optical sources to meet the brightness requirement, thereby satisfying the needs for different degrees of brightness of the projectors. Thus, the laser source in a projector framework adapting an optical source system with a laser source has a great potential to replace the conventional ultra high pressure lamp and become the new optical source of the mainstream projectors.
Generally speaking, laser projectors use a plurality of laser arrays and focuses laser on a phosphor layer to achieve a sufficient fluorescent intensity for output. However, as the demand to the output brightness of the laser projectors gradually increases, the input laser power needs to increase as well. Furthermore, as the input laser power increases, a laser conversion efficiency may decrease due to over-concentration of laser energy. Therefore, the laser energy converted into thermal energy at the phosphor layer increases, making the temperature of the phosphor layer increases, which may influence a light emitting efficiency of the phosphor.
Generally speaking, in the laser projectors, a diffusion film may be disposed on a path on which a laser beam is transmitted from the laser source to a fluorescent wheel, so as to diffuse a laser light spot and uniform the energy. However, the diffusion film itself may result in loss of energy. In addition, when the laser beam is emitted away from a light emitting surface of the laser beam, there is a difference between a fast axis (i.e. a long axis of the laser beam) and a slow axis (i.e. a short axis of the laser beam) for a divergence angle. In other words, the beam emitted from the light emitting surface of the laser source may be formed in an elliptical cone shape. Therefore, when the laser beam is coupled to the fluorescent wheel, the laser light spot formed on the fluorescent wheel is also in an elliptical cone shape. However, since the diffusion direction of the diffusion film is isotropic, the laser light spot formed on the fluorescent wheel may have a long axis that is overly long, causing difficulty in optical coupling and loss in the energy utilization efficiency.
Taiwan patent No. 1300834 discloses an illumination system including a point light source array, a collimator, and a lens. Taiwan patent publication No. 201215987 discloses a projection apparatus including a light source, a light valve, a light uniforming device, and a lens module. U.S. Pat. No. 8,109,638 discloses a projector including a light source, a modulation area, and a projection lens.